Without limiting the scope of the invention, its background is described in connection with methods of manufacture and use of Guerbet alcohols for oil recovery applications, in particular enhanced oil recovery (EOR).
In natural mineral oil deposits, mineral oil is present in the cavities of porous reservoir rocks which are closed off from the earth's surface by impervious covering strata. The cavities may be very fine cavities, capillaries, pores or the like. Fine pore necks may have, for example, a diameter of only about 1 μm. In addition to mineral oil, including proportions of natural gas, a deposit contains water having a higher or lower salt content.
In mineral oil production, a distinction is made between primary, secondary and tertiary production.
In primary production, after drilling into the deposit, the mineral oil flows by itself under the autogenous pressure of the deposit through the well to the surface.
After primary production, the secondary production is therefore used. In secondary production, in addition to the wells which serve the production of the mineral oil, the so-called production wells, further wells are drilled into the mineral oil-carrying formation. Water is forced through these so-called injection wells into the deposit in order to maintain the pressure or to increase it again. By forcing in water, the mineral oil is slowly forced through the cavities in the formation, starting from the injection well, in the direction of the production well. However, this functions only as long as the cavities are completely filled with oil and the more viscous oil is pushed ahead by the water. As soon as the low-viscosity water breaks through cavities, it flows from this time onward along the path of least resistance, i.e. through the resulting channel, and no longer pushes the oil in front of it.
As a rule, only about 30 to 35% of the amount of mineral oil present in the deposit can be extracted by means of primary and secondary production.
It is known that the mineral oil yield can be further increased by tertiary oil production measures (also known as enhanced oil recovery, EOR). An overview of tertiary oil production is to be found, for example, in Journal of Petroleum Science and Engineering 19 (1998) 265-280. Tertiary oil production includes thermal processes in which hot water or superheated steam is forced into the deposit. As a result of this, the viscosity of the oil is reduced. Gases, such as CO2 and nitrogen, can also be used as a flooding medium.
Tertiary oil production furthermore includes processes in which suitable chemicals are used as assistants for oil production. The situation toward the end of the water flood can be influenced by these and mineral oil held in the rock formation up to that time can also be extracted thereby.
For example, the interfacial tension a between the mineral oil and the aqueous phase can be reduced by the addition of suitable surfactants. This technique is also known as “surfactant flooding”. In particular, surfactants which can reduce σ to values of <10−2 mN/m (ultralow interfacial tension) are suitable for this purpose. In this way, the oil droplets are able to change their shape and can be forced through the capillary openings by the flood water.
The oil droplets can then combine to form a continuous oil layer. This has advantages in two respects: firstly, when the continuous oil layer advances through new porous rock, the oil droplets present there can coalesce with the layer. Furthermore, the oil-water interface is substantially reduced by the combination of the oil droplets to form an oil layer, and surfactant no longer required is therefore released. The surfactant released can then mobilize oil droplets remaining in the formation.
The requirements regarding surfactants for tertiary mineral oil productions differ substantially from requirements regarding surfactants for other applications: suitable surfactants for tertiary mineral oil production should reduce the interfacial tension between water and oil (usually about 20 mN/m) to particularly low values of less than 10−2 mN/m in order to permit sufficient mobilization of the mineral oil. This must take place at the usual deposit temperatures of about 15° C. to about 130° C. and in the presence of water having a high salt content, in particular also in the presence of high proportions of calcium and/or magnesium ions; the surfactants must therefore also be soluble in reservoir water having a high salt content.
U.S. Pat. No. 5,092,405 issued to Prukop (1992) discloses a method of recovering heavy oil from an underground reservoir by surfactant flooding which comprises injecting an aqueous surfactant solution comprising about 0.1% to about 5% by weight of an alkoxylated nonionic or ionic surfactant through an injection well into an underground reservoir containing a heavy oil having an average API gravity below about 20° and a reservoir temperature above about 65.6° F. According to the Prukop patent, the alkoxylated surfactant must have sufficient alkylene oxide groups comprised of ethylene oxide or propylene oxide to have a cloud point above about 37.8° F. and below reservoir temperature, and be water-soluble in the surfactant solution to be injected at a temperature below its cloud point, and have a sufficiently large hydrophobe to be soluble in the reservoir's heavy oil at a temperature equal to or greater than reservoir temperature.
U.S. Pat. No. 7,119,125 issued to O'Lenick et al. (2006) relates to specific compositions made by the sulfation of alkoxylated crude C12 to C40 Guerbet alcohol mixtures that contain between 15% and 50% lower molecular weight alkoxylated alcohols. The polyalkoxy groups comprise ethylene oxide and/or propylene oxide units. According to the '125 patent the lower molecular weight alcohols are the raw material alcohols used to make the Guerbet. Sulfated compositions made from this specific bi-modal distribution have unique emulsification properties and experience minimal chromatographic separation when used in downhole applications. It is suggested to use said mixtures for enhanced oil recovery. However emulsification of crude oil is difficult due to low shear forces in the reservoir.
U.S. Patent Application No. 20080217064 (Stoian and Smith, 2008) discloses a drilling fluid comprising: a non-ionic surfactant including at least one of a branched alcohol ethoxylate and a capped alcohol ethoxylate, a detergent builder and a viscosifier. The non-ionic surfactant includes alkyl polyethylene glycol ethers based on C10-Guerbet alcohol and ethylene oxide.
U.S. Patent Application No. 20090270281 (Steinbrenner et al., 2009) describes the use of a surfactant mixture comprising at least one surfactant having a hydrocarbon radical composed of from 12 to 30 carbon atoms and at least one cosurfactant having a branched hydrocarbon radical composed of from 6 to 11 carbon atoms for tertiary mineral oil extraction. According to the Steinbrenner invention, the surfactants (A) are used in a mixture with at least one cosurfactant (B) which has the general formula R2—O—(R3—O)n—R4, where the R2, R3 and R4 radicals and the number n are each defined as follows: n is from 2 to 20, R2 is a branched hydrocarbon radical which has from 6 to 11 carbon atoms and an average degree of branching of from 1 to 2.5, R3 are each independently an ethylene group or a propylene group, with the proviso that the ethylene and propylene groups—where both types of groups are present—may be arranged randomly, alternately or in block structure, R4 is hydrogen or a group selected from the group of —SO3H, —PO3H2, —R5—COOH, —R5—SO3H or —R5—PO3H2 or salts thereof, where R5 is a divalent hydrocarbon group having from 1 to 4 carbon atoms.